The present invention relates to plastic pails and lids therefor for carrying hazardous materials and the like.
A number of plastic pails for carrying hazardous materials and the like are known. Most have flat or nearly flat pail bottoms. Some have circular support members of protectors extending down from the floor at the center thereof, surrounding and protecting the gate, which is the small raised sharp nub where the plastic material was injected and which forms a weak area of the pail. A circular protector is shown, for example, in U.S. Pat. No. 3,516,571 ('571). (This and each of the other patents and publications mentioned anywhere in this disclosure hereby are incorporated by reference in their entireties.) The lids for the prior art pails are also generally flat on top. Some snap into place in a removable sealing engagement such as those shown in the '571 patent and in U.S. Pat. Nos. 3,515,306, and 3,770,156. A screw-on lid manufactured by Container Products of Southfield, Mich. and described in their four-page color brochure entitled "Samson Screw-Top Top Pails" is also known.
These pails when designed to be used for carrying hazardous materials must meet certain governmental requirements, including those of the U.S. Department of Transportation, such as DOT-35, and/or the United Nations specifications. The UN specifications are effective in the United States in 1994, and until then pails can meet either the DOT or the UN specification. While the DOT specifications are structure specific such as specifying minimum wall thicknesses and so forth, the UN specifications are performance based and include certain tests which the pail must pass including a drop test, a vibration test and a stack test. The certification tests for solid wastes are generally speaking less stringent than those for liquid wastes.
After the hazardous wastes have been packaged in the pails and the lids secured to them, the loaded pails must be transported to the desired location and the waste therein disposed of in some environmentally acceptable manner. One appealing disposal method, which has been further developed by Cadence Chemical Resources, Inc. of Michigan City, Ind., is described in the article entitled "Cadence Chemical Resources, Inc., Company Develops New Solid Waste Fuel Process," EI Digest, September 1989, and in the brochure available from Southdown, Inc. of Houston, Tex., and entitled "A Cement Kiln Doesn't Just Destroy Hazardous Waste, It Also Recovers Energy from Them." According to this process the lid, the pail and the hazardous wastes therein are all dropped into a cement kiln at a specific location in the kiln process. The hazardous waste is not only destroyed but actually advantageously creates a fuel that can replace 20-50% of the coal that is used to heat a typical cement kiln. Solid hazardous materials are first blended by a process patented by Cadence to make them a more efficient fuel; the hazardous waste is mixed enough to obtain a consistent BTU output when the pail and wastes are burned. There is also no resulting toxic solid or gaseous wastes from this cement kiln burning. The temperature in the kiln reaches approximately 3700.degree., and thus the waste breaks apart chemically. The organic compounds are destroyed and the inorganic compounds bond with the raw material in the kiln to form the cement clinker. The clinker when it leaves the kiln is cooled, mixed with gypsum, ground into a fine cement powder and then trucked to ready-mix concrete makers, as is known in the art.
Examples of waste materials which can be used with the Cadence process include paint thinners, printing inks, pain residues, industrial cleaning solvents and sludges. And an example of a sludge is the residue left at the bottom of coal ponds. Coal mines typically filter the mine gases through an adjacent pond, and the bottoms of these ponds become toxic after many years of use and need to be cleaned up. The toxic dirt or sludge after being scraped off the bottom of the ponds, then needs to be transported and then typically burned.
The pails of hazardous waste can be palletized and transported in a stacked arrangement to the location of the cement kiln where they are unloaded and transported individually on roller conveyors. There they are dropped through a feed tube to the desired location in the kiln. If the pails have wire handles the handles tend to get hung up on the feed tubes. When transported to the location of the kiln, the loaded and lid-sealed pails are typically stacked on conventional wooden pallets, typically two or three pails high and in a 3.times.3 square or a 3.times.4 rectangle. After being stacked they are shrink wrapped to hold them together. The shrink wrapping process involves simply taking a large piece of Saran wrap type of material, hooking the end onto the pallet, walking with the roll around the loaded and stacked pails, ripping it off and tucking the ends into place. Although the shrink wrap may overlap the top or bottom of the pallet stack, it typically is not wrapped around the top or bottom of the pallet or stacked pails. This wrapping can be done manually or mechanically. The loaded pallets may also be stacked two pallets high when being warehoused.
One known pail, the "ROPAC" pail available from Schoeller, has flat surfaces projecting out from the sidewalls of the pails and having friction surfaces thereon. These flat surfaces then mate with flat surfaces of adjacent pails to keep the pails fixed relative to one another when transported on the pallets. The flat-against-flat contact provides a more stable load because of small locking mechanisms or friction grips.
Problems in the past have occurred though in this transporting of the loaded pails, as from the processors to the kilns. Internal pressures often develop in the pails because of the chemical reactions of the hazardous wastes in them. These pressures according to one rough estimate can be on the order of two, three or even six psi. These pressures with the prior art snap-on lid type pails cause the tops of the lids and the bottoms of the pails to dome outwardly. At a certain point the doming becomes so severe that when one pail is stacked on top of another the two domed or spherical shaped surfaces of the lid on the bottom pail and the floor on the top pail meet. This forms an unstable stack, similar to trying to balance one ball on top of another. Additionally, when they are not stacked and are being transported on a roller conveyor, the downwardly domed floor can get caught in the roller conveyor or at least not travel well along it. The circular gate protector can also be caused to extend downwardly and get caught or impacted. Further, if the internal pressure reaches a certain high level the snap on lid can dome up to such an extent that it loses its seal around the top of the pail and pops off.
Before the pails are loaded into the kiln every so many pails must be checked to make sure its contents are proper and a lid then placed back on it. The processor may also want to reenter the pail to compact its bulky lightweight contents to maximize content weight, before transporting to the kiln. One technique is to physically cut the vertical wall around the circumference to allow removal of the lids. Another method is to use a lever device such as the plastic lever opener of Consolidated Plastics Co., Inc. (216-425-3900; reorder 33434) which has its handle and fulcrum at opposite tool ends and its pry hook between them, thereby limiting the moment arm and the leverage available.